1. Field of the Invention
The present invention relates to a blood flowmeter for measuring an amount of blood flow, a blood amount, a blood flow speed and a pulse of a living body by using scattered light reflected from the living body.
2. Description of the Related Art
In our aging society, there has been a growing interest to a blood flowmeter which can measure circulation of blood which closely relates to adult diseases. Especially, a laser blood flowmeter receives attention in the sense that it can measure the blood flow in capillaries of peripheral tissue without invasion since the laser blood flowmeter has much higher resolution than that of a ultrasound blood flowmeter, wherein measuring the blood flow in capillaries of peripheral tissue was difficult by the ultrasound blood flowmeter. For example, Dennis Watkins and G. Allen Holloway, Jr., An Instrument to measure cutaneous blood flow using the Doppler shift of laser light, IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, Vol. BME-25, No. 1, Jan. 28–33 (1978) discloses a conventional blood flowmeter.
FIG. 1 shows a block diagram of the conventional blood flowmeter in the above-mentioned document. As shown in FIG. 1, a lens 2 is provided near a helium-neon laser 1 which is a light source, one end of an optical fiber 3 for floodlighting is provided near the lens 2, the other end of the optical fiber 3 is held by a holder 4, the holder 4 holds one end of the optical fiber 5 for receiving light, a photodiode 6 is provided near the other end of the optical fiber 5, a preamplifier 7 (40 Hz–40 kHz) is connected to the photodiode 6, and a signal is output via an amplifier 8. The photodiode 6 and the preamplifier 7 are a part of a measuring part for obtaining blood flow speed in tissue of a living body by receiving scattered light reflected from the tissue of the living body.
The blood flow speed is measured by the blood flowmeter shown in FIG. 1 by detecting (heterodyne detection) interference light between scattered light reflected from still tissue of the living body and scattered light reflected from red blood cells (scattered particles) which move in the capillaries in the tissue of the living body, that is, by detecting (heterodyne detection) interference light between scattered light reflected by still tissue of the living body and scattered light whose frequency is shifted due to the Doppler effect related to blood flow speed.
However, according to such a conventional blood flowmeter, since it uses optical fibers 3 and 5, it becomes large, and, since it is necessary to handle the optical fibers 3 and 5, it is difficult to attach the blood flowmeter to a living body for a long time and it is difficult to move with the blood flowmeter on. In addition, since the optical fibers 3 and 5 are provided between the helium-neon laser 1 and a subject part to be measured, the blood flowmeter is susceptible to environmental change. For example, when the optical fiber vibrates even slightly, a measurement result is affected. In addition, since the blood flowmeter is manufactured by assembling the individual optical parts such as the helium-neon laser 1, the optical fibers 3 and 5, and the photodiode 6 three-dimensionally, tuning the optical axis is necessary and manufacturing cost is high.
In addition, as conventional technologies, there are technologies disclosed in Japanese laid-open patent application No. 1-160531 “blood flow speed detector” (Hitachi), and Japanese laid-open patent application No. 10-94527 (Patent No. 3150911) “blood flow amount meter” (Biomedical Science). However, according to the technologies disclosed in these documents, there is a problem in that the degree of downsizing and the accuracy of measurement are not enough.